1. Field of the Invention
The present invention relates generally to an actuator for rotating a rotary member about a rotational axis thereof, and in particular, to an actuator especially suited for actuating a throttle valve of an automotive vehicle to provide a cruise control operation for driving the vehicle at a constant speed.
2. Description of the Prior Art
Various actuators are known and have been used in automotive vehicles for actuating the throttle valves. An example of a prior actuator can be found in Japanese Utility-model Laid-open publication No. 63-173554, which includes a mechanism for reducing the rotational speed of a motor. The actuator also includes an output rotary member which has a solenoid disposed at a position remote from a rotational axis of the motor, and a throttle cable disposed in the vicinity of the rotational axis to open and close a throttle valve. The actuator further includes an input gear member which has a magnetic member disposed at a position to be attracted to the solenoid, and which rotates in meshed relationship with the speed reducing mechanism. When the solenoid attracts the magnetic member, the rotation of the motor is transmitted to the speed reducing mechanism, the input gear member, and the output rotary member, then the opening angle of the throttle valve is controlled via the throttle cable.
However, according to the prior actuator as described above, the solenoid is rotated in accordance with the rotation of the motor, so that lead wires for supplying electric power to the solenoid are moved to follow the rotation of the solenoid. Therefore, if the lead wires are caught by something and prevented from moving along with the solenoid, they may be damaged. In order to avoid this, may be employed a conductor which is electrically connected to an electric source and which has such a configuration to conform to the rotational locus of the solenoid, and also a brush which slides on the conductor to be electrically connected to the solenoid. In this case, however, since the conductor and the brush move in sliding contact with each other, the durability and reliability are deteriorated. Furthermore, since the solenoid is rotated, larger space is needed and the actuator as a whole becomes bigger, comparing with the above-described prior actuator.
With respect to the solenoid-operated actuator as described above, sometimes it is difficult to disconnect the solenoid and magnetic member, even if the excitation of the solenoid is terminated after they were attracted by exciting the solenoid, because of the attracting force caused by the residual magnetism and small electric potential difference. This phenomenon is, of course, inappropriate for the actuator, because the input gear member and output rotary member can not be disconnected.